Optical system for optical projectors



Dec. 24, 1963 T. s. BIRD OPTICAL SYSTEM FOR OPTICAL PROJECTORS FiledSept. 19, 1961 JNVENTOR. THpMAs BY S. BIRD ATTORNEY nited States PatentOfilice lZo-rlr Sept. 19, 1961, Ser. No. 139,3tll

2 Claims. (Cl. 3857) This invention relates to an optical system foroptical projectors and more particularly it relates to a catadioptricrelay system which is particularly adapted for use in contourprojectors.

in general, the optical systems for contour projectors and the likewhich include an optical relay system are characterized by great axiallength so that the resulting overall dimensions of the projector arenecessarily unduly large. This cond ion means that large areas of flooror bench space m ct be used and crowding of usable shop 5;: cc may becaused thereby.

it is an object of this invention to provide an optical relay system ofcomparatively short or moderate axial lcn th so that apparatus in whichthe system is used, such contour projectors, may be reduced in exteriordimenanbull; as well as the cost thereof.

A further object of this invention is to provide such optical relaysystem whereby the point to point ma nificatron of the image formedthereby is strictly constant and Without distoi n for unitymagnification as well as near unity magnification, said system beingcorrected in a superior manner for spherical and chromatic aberrati c.and flatness of field.

Further objects and advantages will be apparent to those skilled in theart by reference to the specification herebclow taken together with theaccompanying drawin which,

EEG. l shows an optical diagram or" one form of optical re ay systemconstructed according to my invention and, 1G. 2 is a view similar toFIG. 1 showing a second form or my invention.

Relay optical systems of the general type herebelow described are shownthe patent application Ser. No.

38,983 of Richard Altman, filed September 18, 1961,

ued to the san -e assignee as the present application he present aication discloses the constructional it" res of a plura y of preferredand practical op al orras in which said relay system may be construeAccording to one such form of optical system wli is generally desi natedby the numeral ll) in FIG. 1, said system comprises a positive lens 11and a spherically curved concave irror 12 I ch is coaxially aligned inconfront g relation tl cod therefrom substantially at the infinity focusof lens As shown schematically in FIG. 1 of the drawing, the opticalsystem it) is so constructed and arranged that an object designated bythe letter O, to be observed is positioned at or within the depth offocus of lens it entirely on one side of and below the common opticalaxis 13 for the lens and mirror.

The free aperture of lens it is divided by any preferred means, such asthe double apertured plate 14 having duplicate apertures 15 and 16, torestrict the passage of the incoming rays from the object O to the areaincluded in the aperture 15. Image rays 17 passing through lens 11strike the concave surface R of the mirror 12 at its center point andare reflected back at 18 at the same reflectance angle as the incidenceangle toward the upper an pass ole mirrors and diaphragrning structuresas long as the basic coniugacy of the object and image is 'ntained.

The obgiect distance and the image distance are denoted l9 and 2%)respectively and are or" equal numerical value when the magnification ofthe image I is unity. The axial 'ace bet sen the apices of the lens 11and mirror 12 represented by the letter D and is numerically actuallyequal to about .98 of the infinity focus of the lens.

In the optical systems here shown and described, the mirror 12 is soconstructed with reference to the other parameters of the system as toact as the aperture stop of said system.

Because of the specific favorable choice of construction parameters forthe lens H and mirror 12 as described hereinafter, a favorable shortoverall distance between the obiect O and the mirror surface R of about1.3 of the infinity focus of the lens is achieved.

Although any preferred form of illumination of object 0 may be used withthe optical system It), episcopic lens 23 eing obliquely directedthrough center of the lower aperture 15 so the entire front surface ofthe object O is illuminated.

For focusing purposes, the lens 11 mirror are in effect rigidlyconnected together as symbolically shown by a bar in FIG. 1 formovements in unison whereby both conjugates of the optical system it?are changed by the sante amount and no change in the distance D or theimage magnification occurs.

Among the outstanding advantages provided by the optical system ill arethe excellent flat field and the near perfect freedom from distortion ofthe image. Additionally a tigrnatism, coma, and all spherical andchromatic aberrations have been corrected to extremely low residualvalues. Since the optical system is used in a comparison or contourprojector, not shown, said system is designed to provide a point topoint magnification over the entire image which is strictly constantthereby re .11-

in a precise reproduction of all contour shapes.

The radius R of the concave reflective surface of the mirror 32 is sochosen as to provide a Petzval sum therefor which is optimumly balancedwith the Petzval sum of the lens ll whereby the aforesaid excellent flatfield is achieved, provided that, in addition, the astigmatism of thelens and mirror is similarly balanced, as in the systems hereindescribed.

In the preferred form of the invention as shown in FIG. 1, the inventorhas determined that the positive lens ll should be an achromat andshould include a negative meniscus element L having lens radii R R and apositive double convex element L having lens radii R and R The negativeelement should have a focal length of substantially -.626f and thepositive element should be substantially +.37f Where 1 represents theinfinity focus of lens ll. The diflerence between the values ofrefractive index of the glass in these two elements should be between.090 and .130 with the higher index in the negative lens element and thedifference between the 1/ values of the two elements should be between23.0 and 35.0.

For acceptable performance, the constructional data for the opticalsystem here disclosed should be within the ranges of values given in thetable herebelow wherein R R and R denote the refractive surfaces, Rdenotes the mirror surface, 1 and t represents the thickness of theindividual lens elements and represents the infinity focus of said lens11.

wherein the minus sign applies to those ray deviating surfaces whichhave their centers of curvature located on the entrant side of thevertex of such surfaces.

A specific successful formulation of constructional data related to anoptical system as shown in FIG. 1 is given in the table herebelowwherein the object and image distances l9 and 20 respectively aresubstantially alike and are equal to substantially .32 and the relativeaperture therefor is f/ 13.0.

wherein D represents the axial distance between lens 11 and mirror 12.The focal length of said negative lens element and said positive lenselement is respectively .626j and +37).

A second form of the invention is shown in FIG. 2 and is generallydesignated by the numeral 30, the constructional data therefor differingsomewhat from FIG. 1 particularly as to the construction of its lens.

Optical system 30 is composed of a positive lens 31 composed of threelens elements in surface contact, which together have an infinity focusof 724.95 mm. Lens 31 is formed of a front negative meniscus lenselement L a central positive double convex lens elements L and a rearnegative lens element L the focal length of L being substantially .573and the focal length of the combination of L and L being substantially+3631.

An object O is positioned at an object distance 32 at or within thedepth of focus of lens 31, similarly to FIG. 1 and therefore theimage-forming rays are transmitted through an aperture 33 in an apertureplate 34 and refracted by the lens 31.

A concave mirror 35 having a spherically curved reflecting surface R islocated coaxially with lens 311 at a distance D which is substantiallyequal to the infinity focus of the lens, D being the axial distancebetween the rear surface of the lens and mirror surface R Image rays 36coming from lens 31 meet at the axis of the mirror surface R and arereflected therefrom along a corresponding oblique path 37 to points onthe lens above its axis. The upper rays 3'7 pass through an aperture 33in aperture plate 34 after refraction by lens 31 to form an image I atan image distance 3% which is conjugate to the object distance 32.

One specific set of values of constructional data for optical system 30which satisfies all of the stated objects of this invention is given inthe table herebelow, wherein R R R and R denote the refractivecurvatures of absolute values wherein the minus sign applies to thoseray deviating surfaces which have their centers of curvature located onthe entrant side of the vertex of such surfaces.

For focusing purposes, lens 31 is connected in any preferred mannerrigidly to the mirror 35 as schematically shown by the connector bar 40so that both optical members travel as a unit.

Although only certain forms of this invention have been shown anddescribed in detail, other forms are possible and changes may be made inthe details and arrangement of the parts thereof without departing fromthe spirit of the invention as defined in the appended claims.

I claim:

1. A catadioptric optical system for use in a comparison projector orthe like which forms an image of an object, said system being afocal andtelecentric and comprising a positive lens and a concave sphericalmirror which is optically aligned in confronting relation therewith andis axially spaced therefrom substantially at the infinity focus of saidlens, said system being so constructed and arranged as to align saidobject on one side of the lens axis within its depth of focus, saidsystem further forming a conjugate image of said object on the same sideof the lens as the object and on the opposite side of said axistherefrom, said lens including a negative and a positive ele mentdesignated L and L respectively, the optical data related to said systembeing given in the mathematical statements herebelow,

absolute values wherein 1 represents the infinity focus of said lens, Rand R denote the radii of the exterior front and rear refrac tivesurfaces respectively of said lens, R denotes the radius of theinterface refractive surface between said negative element and positiveelement, R denotes the radius of said concave mirror, 2 and t denote theaxial thicknesses of said negative and positive elements L and Lrespectively, D represents the axial distance between the apices of theconfronting surfaces R and R and n and 11 represent the refractive indexand Abbe number respectively of the glasses from which the lens is made,the focal lengths of lens elements L and L being respectively .626j and+37] where the minus sign de notes negative focal length whereby animage of superior quality and extreme flatness is produced along with ashort overall length of said system.

2. A catadioptric optical system for use in a comparison projector orthe like which forms an image of an object, said system being afocal andtelecentric and comprising a positive lens member which is composed of afront negative meniscus lens element designated L an intermediate doubleconvex lens element L in contact with element L and a rear negativemeniscus lens element L in contact with element L said system furthercomprising a concave spherical mirror having a surface designated Rwhich is optically aligned with and confronting lens element L; at anaxial distance D therefrom which is substantially equal to the infinityfocal length of the lens member, the object to be projected beingaligned at a conjugate position with the image formed thereof on thesame side of the lens member but laterally displaced therefrom by anequal distance from the lens member axis, the constructional data forthe lens memher and mirror having numerical values as given in the tableherebelow wherein R designates the radius of the front surface of lenselement L R designates the radius of the interface between elements Land L R designates the radius of the interface between elements L and Land R designates the radius of the rear surface of element L the minussign used with the numerical values of the above radii applying to thosesurfaces which have their centers of curvature lying on the entrant sideof the vertices of said surfaces, D represents the axial distancebetween said lens member and mirror, t t and r represent the axialthicknesses of the lens elements L L and L respectively, 11 and 1/represent the refractive index and Abbe number respectively of the lensmaterials, and represents the focal length of said lens member,

-rbsolute values References Cited in the file of this patent UNITEDSTATES PATENTS Chretien Dec. 9, 1930 Altman Apr. 24, 1956 UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent N06 3 115 53 December 241964 Thomas S, Bird It is hereby certified that error ent requiringcorrection and that the s corrected below.n

appears in the above numbered pataid Letters Patent should read asColumn 6 line 161 for "t aO22lf reed 13 @0121? --o Signed and sealedthis 9th day of June 1964,

(SEAL) Attest:

ERNEST We SWIDER EDWARD J BRENNER Commissioner of Patents AttestingOfficer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N063 115 53 December 24 1964 Thomas S, Bird It is hereby certified thaterror ent requiring correction and that the s corrected below.n

appears in the above numbered pataid Letters Patent should read asColumn 6 line 161 for "t aO22lf reed 13 @0121? --o Signed and sealedthis 9th day of June 1964,

(SEAL) Attest:

ERNEST We SWIDER EDWARD J BRENNER Commissioner of Patents AttestingOfficer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent N003 1l5 537 December 24 1964 Thomas S. Bird It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 6 line IO for "t. =,O22lf rea Signed and sealed this 9th day ofJune 19640 (SEAL) Attest:

ERNEST W SWIDER EDWARD J. BRENNER Commissioner of Patents Attes tingOfficer

1. A CATADIOPTRIC OPTICAL SYSTEM FOR USE IN A COMPARISON PROJECTOR ORTHE LIKE WHICH FORMS AN IMAGE OF AN OBJECT, SAID SYSTEM BEING AFOCAL ANDTELECENTRIC AND COMPRISING A POSITIVE LENS AND A CONCAVE SPHERICALMIRROR WHICH IS OPTICALLY ALIGNED IN CONFRONTING RELATION THEREWITH ANDIS AXIALLY SPACED THEREFROM SUBSTANTIALLY AT THE INFINITY FOCUS OF SAIDLENS, SAID SYSTEM BEING SO CONSTRUCTED AND ARRANGED AS TO ALIGN SAIDOBJECT ON ONE SIDE OF THE LENS AXIS WITHIN ITS DEPTH OF FOCUS, SAIDSYSTEM FURTHER FORMING A CONJUGATE IMAGE OF SAID OBJECT ON THE SAME SIDEOF THE LENS AS THE OBJECT AND ON THE OPPOSITE SIDE OF SAID AXISTHEREFROM, SAID LENS INCLUDING A NEGATIVE AND A POSITIVE ELEMENTDESIGNATED L1 AND L2 RESPECTIVELY, THE OPTICAL DATA RELATED TO SAIDSYSTEM BEING GIVEN IN THE MATHEMATICAL STATEMENTS HEREBELOW,